Nitrogen-containing ultramicroporous carbon nanospheres for high performance supercapacitor electrodes

[Ag4Br6] cluster-based 3D bromoargentate hybrid: crystal structure, optical/photoelectrical performance and theoretical study

The self-assembly of cluster-based halide framework materials has been a matter of great interest but with great challenges. Herein, by exploiting hexamethylenetetramine (Hmta) with Td symmetry as a structural modifier, we successfully constructed and systematically characterized an unusual three-dimensional (3D) hybrid bromoargentate, namely K[NH4][Ag4Br6(Hmta)] (1), bearing a diamond-type [Ag4Br6(Hmta)]n2n- anionic skeleton built up from adamantane-like units of inorganic [Ag4Br6] clusters and organic Hmta ligands. UV-Vis diffuse reflectance analysis showed that the optical bandgap of the title compound was 2.68 eV, indicating a visible-light-responsive semiconductive behavior. More importantly, upon alternate light illumination, the so-designed compound exhibited remarkable photoelectric switching properties, with photocurrent densities (0.38 and 1.10 μA cm-2 for visible and full-spectrum light, respectively) that compete well with and even exceed those of some high-performance metal halide counterparts. Further theoretical calculations, including band structure, density of states, and wave functions, revealed that compound 1 has a unique valence band and conduction band distribution, rendering it with small effective masses (especially the electrons), which may be responsible for its good photoelectricity. Furthermore, in this work, Hirshfeld surface analysis, thermogravimetric analysis, and X-ray photoelectron spectroscopy (XPS) studies were performed.

Microstructural tailoring of porous few-layer graphene-like biochar from kitchen waste hydrolysis residue in molten carbonate medium: Structural evolution and conductive additive-free supercapacitor application

Biomass-derived graphene-like material is a promising candidate for supercapacitor electrodes, while it is critical to controllably convert biomass into structure-tunable graphene. Herein, few-layer graphene-like biochar (FLGBS) was successfully fabricated from waste biomass in molten carbonate medium. Molten carbonate acted as the effective catalyst for graphitizing and the liquid medium for microcrystal relinking to achieve the rearrangement of carbon structure. It was found that the stacking of graphene layer and formation of porous structure were influenced by the volume of reaction medium and biomass pre‑carbonation. Namely, increasing the dosage of molten K₂CO₃ was in favor to form few layer-type graphene structure, but excess dosage could destroy the nanopore structure to expand the aperture. In addition, pre‑carbonation at high temperature impeded the exfoliation of graphene layers. When FLGBSs were applied to fabricate conductive additive-free electrode, they displayed a superior supercapacitor performance (up to 237.4 F g^-1 at 0.5 Ag^-1). This excellent performance should be attributed to the large specific surface area, hierarchical pore structure and graphene-like structure. In short, this work could help to get insights into the structural evolution of biomass carbon to graphene-like biochar in molten carbonate medium and achieve the tailoring of microstructure for further application in energy storage.

Enhanced electrochemical performance of porous carbon from wheat straw as remolded by hydrothermal processing

To improve the electrochemical properties of lignocellulose-derived carbon, wheat straw was hydrothermally processed at different temperatures followed by KOH activation for the preparation of porous carbons. Their physical, chemical, and electrochemical properties were analyzed to clarify the effects of hydrothermal processing. The results indicated that high-temperature hydrothermal processing fragmented the wheat straw and increased the heteroatoms content to make the hydrochars more conducive to activation, thereby improving the specific surface area, N-heteroatoms and phenolic hydroxyl groups of activated carbons. A maximum specific surface area of 2034.4 m² g^-1 was achieved by HAC-300 (the activated carbon derived from hydrothermally processed wheat straw at 300 °C) with more N-heteroatoms and phenolic hydroxyl groups. Correspondingly, the excellent electrochemical performance of the three-electrode supercapacitor device assembled by HAC-300 showed a specific capacitance of 286.95 F g^-1 at 0.5 A g^-1, representing an improvement of 89.5 % over than that of the original wheat straw without hydrothermally processing. Its symmetric supercapacitor also realized a good capacitance retention of 95.8 % after 10,000 cycles at 5 A g^-1, suggesting the excellent cycling stability of the porous carbon from the hydrothermally processed wheat straw.

High mass load of oxygen-enriched microporous hollow carbon spheres as electrode for supercapacitor with solar charging station application

Carbon materials modified with pores and heteroatoms have been pursued as promising electrode for supercapacitors due to the synergic storage of electric double-layer capacitance (EDLC) and pseudocapacitance. A vital problem that the actual effect of pores and heteroatoms on energy storage varies with the carbon matrix used presents in numerous carbon electrodes, but is ignored greatly, which limits their sufficient utilization. Moreover, most of modified carbon electrodes still suffer from severe capacitance degeneration under high mass load caused by the blocked surface and inaccessible bulk phase. Here, we shape an interconnected hollow carbon sphere (HCS) as the matrix by regulating and selectively-etching low molecular weight component in the inhomogeneous precursors, accompanied with the decoration of rich oxygen groups (15.9at%) and micropores (centering at 0.6-1.4 nm). Finite-element calculation and energy storage kinetics reveal the modified HCS electrode exposes accessible dual active surface with highly-matched electrons and ions for pores and oxygen groups to improve both EDLC and pseudocapacitance. Under a commercial-level load of 11.2 mg cm^-2, the HCS exhibits a high specific capacitance of 288.3 F g^-1 at 0.5 A g^-1, performing a retention of 91.8% relative to 314 F g^-1 under 2.8 mg cm^-2 load, applicable for solar charging station to efficiently drive portable electronics.

Boron and nitrogen co-doped carbon nanospheres for supercapacitor electrode with excellent specific capacitance

At present, carbon materials derived from biomass precursors have many limitations in the field of energy storage. In this study, boron and nitrogen (B/N) co-doped carbon nanospheres are successfully prepared by emulsion crosslinking method using chitosan and boric acid as raw materials. After carbonization at high temperature, the carbon nanospheres can be facilely prepared with controllable particle size, showing excellent structural stability and sphericity. In addition, the heteroatoms co-doping endows the carbon nanospheres with large specific surface area, high graphitization degree and excellent electrochemical performance. Applying the carbon nanospheres for supercapacitors, the specific capacitance can reach up to 336.7 F g^-1at a current density of 1 A g^-1. Even after 10,000 cycles, the Coulomb efficiency and specific capacitance still remain at 98.61% and 96.8%, respectively, demonstrating the great promise of B/N co-doped carbon nanospheres for the state-of-the-art supercapacitor electrodes applications.

An ultrasensitive luteolin electrochemical sensor based on a glass carbon electrode modified using multi-walled carbon nanotube-supported hollow cobalt sulfide (CoSx) polyhedron/graphene quantum dot composites

Fabrication of an electrochemical luteolin sensor composed of multi-walled carbon nanotube-supported hollow cobalt sulfide (CoSx) polyhedrons/graphene quantum dots and its application in actual sample detection.

Hollow porous nitrogen-doped carbon embedded with ultrafine Co nanoparticles boosting lithium-ion storage

Hollow porous nitrogen-doped carbon embedded with ultrafine Co nanoparticles (Co@NC) was synthesized by a facile self-template strategy, which exhibited excellent cycling stability and remarkable rate performance.

Renaissance of Stöber method for synthesis of colloidal particles: New developments and opportunities

Colloidal silica particles have received a widespread interest because of their potential applications in adsorption, ceramics, catalysis, drug delivery and more. Among many approaches towards fabrication of these colloidal particles, Stöber, Fink and Bohn (SFB) method, known as Stöber synthesis is an effective sol-gel strategy for production of uniform, monodispersed silica particles with highly tailorable size and surface properties. This review, after a brief introduction showing the importance of colloidal chemistry, is focused on the Stöber synthesis of silica spheres including discussion of the key factors affecting their particle size, porosity and surface properties. Next, further developments of this method are presented toward fabrication of polymer, carbon, and composite spheres.

Cobalt and nitrogen co-doped porous carbon/carbon nanotube hybrids anchored with nickel nanoparticles as high-performance electrocatalysts for oxygen reduction reactions

Non-precious metal-nitrogen-carbon (MNC) materials have been recognized as alternatives to noble-metal catalysts, such as Au/C, Pt/C and Ru/C. As the precursors of MNC catalysts, carbonized zeolite imidazole frameworks (ZIFs) have been widely studied due to their porosity and the composition of ligands, including carbon and nitrogen. Herein, we successfully synthesize a non-precious metal-based ORR catalyst with nickel nanoparticles anchored on cobalt and nitrogen co-doped porous carbon/carbon nanotubes (Ni/Co-NC), employing ZIF-67 metal-organic frameworks as precursors. The Ni/Co-NC catalyst shows an excellent onset potential of 0.984 V and a half-wave potential of 0.869 V in 0.1 M KOH, comparable to those of commercial Pt/C. The excellent ORR performance of Ni/Co-NC was attributed to the synergistic coexistence of the atomically dispersed metal species coordinated with nitrogen (metal-N sites) and carbon-encapsulated nickel nanoparticles as well as the hierarchical porous structure in the catalyst. In addition, the Ni/Co-NC catalyst possesses outstanding anti-poisoning capacity and long-term duration against methanol crossover in an alkaline environment. The obtained results enable the Ni/Co-NC catalyst to explore potential applications in energy conversion and storage systems.

Ionic liquid-induced tunable N-doped mesoporous carbon spheres for supercapacitors

N-Doped mesoporous carbon spheres with tunable structures have been prepared by a feasible co-assembly under the induction of an ionic liquid for supercapacitors.

Heteroatom-doped hollow carbon spheres made from polyaniline as an electrode material for supercapacitors

In this work, novel heteroatom-doped hollow carbon spheres (HHCSs) were prepared via the carbonization of polyaniline hollow spheres (PHSs), which were synthesized by one-pot polymerization. It was found that the carbonized PHSs at 700 °C exhibit high specific capacitance of 241 F g⁻¹ at a current density of 0.5 A g⁻¹ and excellent rate capability. The excellent electrochemical performance can be attributed to the heteroatom-doping and hollow carbon nanostructure of the HHCSs electrodes. Heteroatom groups in the HHCSs not only improve the wettability of the carbon surface, but also enhance the capacitance by addition of a pseudocapacitive redox process. Their unique structure provides a large specific surface area along with reduced diffusion lengths for both mass and charge transport.

In this work, novel heteroatom-doped hollow carbon spheres (HHCSs) were prepared via the carbonization of polyaniline hollow spheres (PHSs), which were synthesized by one-pot polymerization.

ZIF-67-Derived N-Doped Co/C Nanocubes as High-Performance Anode Materials for Lithium-Ion Batteries

Co nanoparticles embedded in nitrogen-doped carbon nanocubes (Co/NCs) for applications as anode materials in rechargeable lithium-ion batteries were synthesized by calcining Co-based metal-organic framework. Sizes of Co nanoparticles were ∼15 nm according to X-ray diffraction (XRD) and transmission electron microscopy. Electrochemical performances of the as-prepared anode nanocube composite at 700 °C showed a high initial capacity of 1375.1 mAh g^-1 in the voltage range of 0.01-3.0 V at the current rate of 0.1 A g^-1. After 100 cycles, capacity remained at 688.6 mAh g^-1. Thereinto, the role of Co nanoparticles in electrochemical reaction was also elucidated by in situ XRD experiment. Capacity increase of Co/NCs at the high currents was observed, which are potentially caused by the activation of electrode and pseudocapacitance during cycling. High surface area and abundant mesopores contributed to the improved electrochemical performances of the anode, providing numerous pathways and sites for Li⁺ transfer and storage and accordingly contributing to pseudocapacitance capacity.

The fabrication of a 3D current collector with bitter melon-like TiO2-NCNFs for highly stable lithium-sulfur batteries

The conductive 3D freestanding N-doped carbon nanofibers (NCNFs) current collector was embedded with homogeneously polar TiO₂ nanoparticles. This current collector used for the sulfur cathode exhibits strong chemical adsorption for hindering the shuttle effect of polysulfides, and demonstrates a high specific capacity of 865 mA h g^-1 at 0.2C and excellent cycle performance (200 cycles with capacity retention of 91%).

Facile Synthesis of Nitrogen-Doped Microporous Carbon Spheres for High Performance Symmetric Supercapacitors

Nitrogen-doped microporous carbon spheres (NMCSs) are successfully prepared via carbonization and KOH activation of phenol-formaldehyde resin polymer spheres synthesized by a facile and time-saving one-step hydrothermal strategy using triblock copolymer Pluronic F108 as a soft template under the Stöber-like method condition. The influence of the ethanol/water volume ratios and carbonation temperatures on the morphologies, pore structures and electrochemical performances of the prepared NMCSs are investigated systematically. The optimal NMCSs have a large specific surface area of 1517 m2 g- 1 with a pore volume of 0.8 cm3 g- 1. The X-ray photo-electron spectroscopy analysis reveals a suitable nitrogen-doped content of 2.6 at.%. The as-prepared NMCSs used as supercapacitor electrode materials exhibit an outstanding specific capacitance of 416 F g- 1 at a current density of 0.2 A g- 1, also it shows an excellent charge/discharge cycling stability with 96.9% capacitance retention after 10,000 cycles. The constructed symmetric supercapacitors using PVA/KOH as the gel electrolyte can deliver a specific capacitance of 60.6 F g- 1 at current density of 1 A g- 1. A maximum energy density of 21.5 Wh kg- 1 can be achieved at a power density of 800 W kg- 1, and the energy density still maintains 13.3 Wh kg- 1 even at a high power density of 16 kW kg- 1. The results suggest that this work can open up a facile and effective way to synthesize the NMCSs for electrode materials of high performance energy storage devices.

Insight into Sulfur Confined in Ultramicroporous Carbon

Here, we provide a deeper insight into the state of sulfur confined in ultramicroporous carbon (UMC) and clarify its electrochemical reaction mechanism with lithium by corroborating the results obtained using various experimental techniques, such as X-ray photoelectron spectroscopy, electron energy loss spectroscopy, in situ Raman spectroscopy, and in situ electrochemical impedance spectroscopy. In combination, these results indicate that sulfur in UMC exists as linear polymeric sulfur rather than smaller allotropes. The electrochemical reactivity of lithium with sulfur confined in UMC (pore size ≤0.7 nm) is different from that of sulfur confined in microporous carbon (≤2 nm, or ultramicroporous carbon containing significant amount of micropores) and mesoporous carbon (>2 nm). The observed quasi-solid-state reaction of lithium with sulfur in UMC with a single voltage plateau during the discharge/charge process is due to the effective separation of solvent molecules from the active material. The size of carbon pores plays a vital role in determining the reaction path of lithium with sulfur confined in UMC.

Preparation of boron-doped mesoporous carbon with aromatic compounds as expanding agents

Boron-doped ordered mesoporous carbon (B-OMC) was synthesized using the aromatic compounds benzene, 1,3,5-trimethylbenzene, 1,3,5-triethylbenzene and 1,3,5-triisopropylbenzene as expanding agents. The expanding mechanism as well as the effect of the expanding agent molecule on the properties of B-OMCs were studied. Compared with the unmodified one, the order of B-OMCs treated with aromatic compounds is improved significantly. In addition, along with the increase in hydrophobicity and steric hindrance of the expanding agents, the pore size and pore volume of B-OMCs increase, while their surface area and specific capacitance increase first, and then drop off slightly. The obtained B-OMC-TEB has a high boron content (1.54 wt%), the largest surface area (693 m² g⁻¹), a much better electrochemical performance and the highest specific capacitance (290 F g⁻¹), 30% higher than that of ordinary B-OMC. Furthermore, the specific capacitance can be maintained at 155 F g⁻¹ even at a high current density of 20 A g⁻¹, indicating that it has a high capacitance retention rate.

TMB, TEB and TiPB exhibit both penetration and swelling effects, and the pore size of B-OMCs increases with their increasing hydrophobicity.

Facile synthesis of bio-based nitrogen- and oxygen-doped porous carbon derived from cotton for supercapacitors

Biomass-derived O- and N-doped porous carbon has become one of the most competitive supercapacitor electrode material because of its renewability and sustainability.

Carboxymethylcellulose ammonium-derived nitrogen-doped carbon fiber/molybdenum disulfide hybrids for high-performance supercapacitor electrodes

In this paper, a new type of nitrogen-doped carbon fiber/molybdenum disulfide (N-CFs/MoS₂) hybrid electrode materials are prepared via a certain concentration in solvothermal synthesis followed by a high-temperature carbonization process and using the carboxymethylcellulose ammonium (CMC-NH₄) as a structure-directing agent for MoS₂ nanosheet growth during the solvothermal synthesis process. The addition of CMC-NH₄ effectively prevents the agglomeration of MoS₂ nanosheets to increase the specific surface area. Moreover, it not only serves as a carbon source to provide conductive pathways, but also introduces N atoms to improve the conductivity of the CFs and promote the transfer of electrons and ions. This ultimately increases the conductivity of the electrode materials. Thus, the as-prepared N-CFs/MoS₂ hybrids exhibit excellent electrochemical performance. The specific capacitance is up to 572.6 F g⁻¹ under a current density of 0.75 A g⁻¹ and the specific capacitance retained 98% of the initial capacitance after 5000 cycles of charge–discharge tests at a current density of 2.5 A g⁻¹. Moreover, the hybrids show a maximum energy density of 19.5 W h kg⁻¹ at a power density of 94 W kg⁻¹. Therefore, the as-prepared N-CFs/MoS₂ hybrids with remarkable electrochemical properties, low cost and environment protection show potential for practical application in the development of high-performance electrochemical energy storage devices.

Novel CMC-NH₄-derived nitrogen-doped CFs/MoS₂ hybrid electrode materials are prepared using CMC-NH₄ as a structure-directing agent for MoS₂ nanosheets.

Fabrication of carbon nanospheres by the pyrolysis of polyacrylonitrile-poly(methyl methacrylate) core-shell composite nanoparticles

Carbon nanospheres with a high Brunauer-Emmett-Teller (BET) specific surface area were fabricated via the pyrolysis of polyacrylonitrile-poly(methyl methacrylate) (PAN-PMMA) core-shell nanoparticles. Firstly, PAN-PMMA nanoparticles at high concentration and low surfactant content were controllably synthesized by a two-stage azobisisobutyronitrile (AIBN)-initiated semicontinuous emulsion polymerization. The carbon nanospheres were obtained after the PAN core domain was converted into carbon and the PMMA shell was sacrificed via the subsequent heat treatment steps. The thickness of the PMMA shell can be easily adjusted by changing the feeding volume ratio (FVR) of methyl methacrylate (MMA) to acrylonitrile (AN). At an FVR of 1.6, the coarse PAN cores were completely buried in the PMMA shells, and the surface of the obtained PAN-PMMA nanoparticles became smooth. The thick PMMA shell can inhibit the adhesion between carbon nanospheres caused by cyclization reactions during heat treatment. The carbon nanospheres with a diameter of 35-65 nm and a high BET specific surface area of 612.8 m²/g were obtained from the PAN-PMMA nanoparticles synthesized at an FVR of 1.6. The carbon nanospheres exhibited a large adsorption capacity of 190.0 mg/g for methylene blue, thus making them excellent adsorbents for the removal of organic pollutants from water.

Nitrogen-Doped Mesoporous Carbons for Supercapacitor Electrodes with High Specific Volumetric Capacitance

To pursue the miniaturization of supercapacitors in practical use, it is critical to construct an efficient but limited porosity of a nanocarbon-based electrode for simultaneously obtaining a high utilization of energy storage places and high coating density. However, current studies dominantly focus on the enhancement of specific mass capacitance (C_m) by increasing the pore volume and surface area, leading to a low coating density and, thereby, resulting in a low specific volumetric capacitance (C_V). We report herein the fabrication of a nitrogen-doped mesoporous carbon (NNCM), whose tunable pore volume coupled with the fixed mesopore size offers us the possibility to control the coating density, thus optimizing the C_V and C_m for different application purposes. As a result, NNCM with the highest pore volume and surface area of 2.11 cm³ g^-1 and 663 m² g^-1 demonstrates the highest C_m (190 F g^-1) but lowest C_V (124 F cm^-3) because the overhigh porosity reduces the coating density greatly. NNCM with moderate pore volume and surface area of 1.22 cm³ g^-1 and 489 m² g^-1 shows the highest C_V of 200 F cm^-3, although it presents a low C_m of 147 F g^-1. These results may raise concerns about constructing a suitable porosity to realize a target-oriented use, particularly those targeting miniaturized devices.

Molybdenum Carbide-Derived Chlorine-Doped Ordered Mesoporous Carbon with Few-Layered Graphene Walls for Energy Storage Applications

In this work, we propose a one-step process to realize the in situ evolution of molybdenum carbide (Mo₂C) nanoflakes into ordered mesoporous carbon with few-layered graphene walls (OMG) by chloridization and self-organization, and simultaneously the Cl-doping of OMG (OMG-Cl) by modulating chloridization and annealing processes is fulfilled. Benefiting from the improvement of electroconductivity induced by Cl-doping, together with large specific surface area (1882 cm² g^-1) and homogeneous pore structures, as anode of lithium ion batteries, OMG-Cl shows remarkable charge capacity of 1305 mA h g^-1 at current rate of 50 mA g^-1 and fast charge-discharge rate within dozens of seconds (a charge time of 46 s), as well as retains a charge capacity of 733 mA h g^-1 at a current rate of 0.5 mA g^-1 after 100 cycles. Furthermore, as a promising electrode material for supercapacitors, OMG-Cl holds the specific capacitances of 250 F g^-1 in 1 M H₂SO₄ solution and 220 F g^-1 at a current density of 0.5 A g^-1 in 6 M KOH solution, which are ∼40% and 20% higher than those of undoped OMG electrode, respectively. The high capacitive performance of OMG-Cl material can be due to the additional fast Faradaic reactions induced from Cl-doping species.

Sorghum core-derived carbon sheets as electrodes for a lithium-ion capacitor

A lithium-ion capacitor with high energy and high power is fabricated using sorghum core-derived carbon sheets as both electrodes.

Winter-jujube-derived carbon with self-doped heteroatoms and a hierarchically porous structure for high-performance supercapacitors

The synthesized JC samples possessed abundant self-doped heteroatoms and hierarchically porous structures (the co-existence of micro-, meso-, and macropores).

Mesopore-dominant wormhole-like carbon with high supercapacitive performance in organic electrolyte

The suitable mesopore size of 3.1 nm offers a large ion-accessible surface area for WMC, thus obtaining superior supercapacitive performance.

Nitrogen- and oxygen-containing micro–mesoporous carbon microspheres derived from m-aminophenol formaldehyde resin for supercapacitors with high rate performance

Nitrogen- and oxygen-containing micro–mesoporous carbon microspheres derived from m-aminophenol formaldehyde resin were prepared by the hydrothermal synthesis/carbonization/activation route for high-rate performance supercapacitor application.